Secondary batteries called lithium ion batteries are currently attracting attention. They can broadly be classified into two categories of so called lithium ION secondary batteries and lithium METAL secondary batteries. The lithium METAL secondary batteries utilize precipitation and dissolution of lithium for the operation. Besides, the lithium ION secondary batteries utilize storage and release of lithium in the charge-discharge reaction. These batteries both can realize charge-discharge at large energy densities as compared with lead batteries or nickel-cadmium batteries. By making use of this characteristic, in recent years, these batteries have been widely applied to portable electronic equipment such as camera-integrated VTR's (video tape recorders), mobile telephones, and notebook computers. So as to respond to further expansion of applications as to a power source of the portable electronic equipment, the development has been continually progressed to provide lightweight secondary batteries with higher energy densities. Nonetheless, there exists a strong demand for size reduction, service life prolongation, and safety enhancement.
Regarding a liquid electrolyte to be used in lithium ion secondary batteries or lithium metal secondary batteries (hereinafter, these may be collectively referred to simply as a lithium secondary battery), a particular combination of materials has widely been employed in order to realize high electric conductivity and potential stability. That is, a carbonic acid ester-based solvent like propylene carbonate or diethyl carbonate is employed, in combination with an electrolyte salt of lithium hexafluorophosphate or the like.
With respect to the composition of a liquid electrolyte, for the purpose of improving battery characteristics, technique is variedly proposed as to additives to be contained in a liquid electrolyte. For example, by the additives, it is proposed to form an oxidative polymerized film as a protective film (SEI: Surface Electrolyte Interface) on the negative electrode (see Patent Literatures 1 and 2). Besides, it is also attempted to form such a protective film in the positive electrode as revealed in Patent Literatures 3 and 4.